This invention relates in general to imaging and more specifically, to a process of producing multicolor images utilizing color particles having a resin carrier containing electrically photosensitive material.
In one embodiment of the monochromatic manifold imaging system, an imageable member is prepared by coating a layer of cohesively weak photoresponsive imaging material onto a substrate. This coated substrate is called the "donor." In preparation for the imaging operation, the imaging layer is activated, as by treating it with a swelling agent or partial solvent for the material. This step may be eliminated, of course, if the layer retains sufficient residual solvent after having been coated on the substrate from a solution or paste. The activating step provides the dual function of making the top surface of the imaging layer slightly tacky and, at the same time, weakening it structurally so that it can be fractured more easily along a sharp line which defines the image to be reproduced. Once the imaging layer is activated, a receiving sheet is laid down over its surface. An electrical potential is then applied across this manifold set while it is exposed to a pattern of light-and-shadow representative of the image to be reproduced. Upon separation of the donor substrate and receiving sheet, the imaging layer fractures along the lines defined by the pattern of light-and-shadow to which it has been exposed, with part of this layer being transferred to the receiving sheet while the remainder is retained on the donor sheet. Thus, a positive image is generally produced on one while a negative is produced on the other.
The system is capable of producing monochromatic images of excellent density and resolution. If an attempt is made to uniformly mix pigment particles responding to different colors throughout the imaging material, effective strip-out may not be entirely satisfactory since particles of different colors scattered throughout the thickness of the imaging layer may tend to mask each other and prevent stripping of single colors only in desired single colored areas.
To achieve color spearation in a single set imaging system, U.S. Pat. No. 3,556,783, based on a subtractive color system, provides an imaging set in which the imaging material is coated onto the donor substrate as a plurality of small contiguous areas, different areas having at least two different colors which respond to lights of different colors whereby the manifold set will respond to color originals selectively so as to produce a full-color image corresponding to the original. More specifically, the plurality of small contiguous areas is provided by suitable printing methods such as gravure roller, spraying through stencils, and by conventional color lithography. In all of these techniques an ordered arrangement of colors results.
While multicolored images may be produced in the single set system outlined in U.S. Pat. No. 3,556,783, complete color separation remains a continuing problem due to the fracturable nature of the contiguous areas in the imaging layer as well as the difficulty of attaining perfect registration of the colors. In addition, the ordered array of colors in this system may result in the formation of a moire pattern when imaging a halftone photograph or print. The problem of successive halftone imaging is fully detailed in the text entitled "The Printing Industry," Strauss, P. 193-194, published by The Printing Industries of America, Inc. And further, maximum color density could not be attained in the patented system because of the patterned arrangement of the contiguous colors.
A solution to these difficulties is offered in U.S. Pat. No. 3,854,943, where a subtractive imaging mono-layer, sandwiched between donor and receiver members, is comprised of a plurality of randomly mixed agglomerates of at least two different colors which respond selectively to light. The randomly mixed agglomerates respond in an electric field to radiation within their sensitivities by selectively adhering to the receiver during sandwhich separation whereupon each individual agglomerate is easily and independently removed from the imaging layer. While images resulting from this system demonstrate excellent color separation, it is largely confined to the use of pigment agglomerates. The nature of the colors in such a system depends entirely on the brilliancy of the individual pigments. Such systems generally result in low color saturation because of the particulate nature of the color entities. This instant invention attains high color saturation by the use of dyes rather than pigments.
In U.S. Pat. No. 2,940,847 to Kaprelian there is described, among other things, a particle imaging system in which multi-layered particles of dye-filtered photoconductor on a resin core material as utilized, optionally containing a central liquid dye core. However, the imaging layer of this system is three or more particles deep which magnitude results in obvious color separation difficulties. Furthermore, the dyes used in this system are encapsulated for ultimate pressure release onto a suitable absorbent substrate. The use of pressure sensitive capsules in imaging systems is generally undesirable because of the problems in preparation of the imaging particles as well as inconsistency in pressure bursting of the liquid dye particles in obtaining a final image.
In yet another patent, U.S. Pat. No. 3,681,064 to Shu-Hsiung Yeh, there is disclosed a photoelectrophoretic imaging system in which a thin layer of a suspension of particles in a liquid carrier is interpositioned between two electrodes. Imaging takes place by imposing an electric field across the suspension and exposing same through one of the electrodes. The particles in the suspension may be any suitable photosensitive particle and includes multiple layered particles of photosensitive dyes and/or pigments on a resin core material, similar to those in Kaprelian. Additionally, the electrode spacings may be as low as one mil or less which renders the suspension of particles a thin layer of imaging material.
In German Publication OLS No. 2120384 there is disclosed a photoelectrophoretic imaging system in which imaging particles containing colorants are used for the ultimate purpose of rendering an imaged member functional as a spirit master. The imaging particles contain a colorant in the form of a spirit or alcohol soluble dye, the colorant of the master being transferable to a receiver in the presence of the solvent. The dye photoelectrophoretic imaging particles disclosed include dyed photosensitive pigment particles and dyed resin photosensitive pigment particles. As mentioned above, the dyes are ultimately utilized as a colorant in a photoelectrophoretically prepared master.